1. Field of the Invention
Linear Motors can be classified into core and coreless types, according to whether the rotor has a core or not. The present invention relates to a coreless type linear motor, and especially to a coreless linear motor having a better heat dissipation effect.
2. Description of the Prior Art
Rotors of commonly known linear motors are mainly composed of coils and epoxy resin. The coils are used to provide the rotor with a variable magnetic field while the epoxy resin is used to fasten coils. When electric current passes coils of the rotor, a magnetic field is produced and interacts with the magnetic field of the permanent magnet to generate thrust. The manufacturing process of the rotor is to place the coils made of copper wires into the body of the plate-type rotor, and then to use epoxy resin and or other kinds of resin to fill and wrap around the whole coils to increase the strength of the rotor. Because a substantial part of the energy generated by electromagnetic interaction is transformed into heat energy, the temperature of the coil rises which causes the electric resistance of the coils to rise. In this way, the electric current value of the coils is reduced, thereby decreasing the efficiency of the rotor and limiting the maximum thrust. In addition, variation of temperature also results in some problems, such as expansion and shrinkage of material, which causes the assembly of the parts to be too tight or too loose.
Commonly known methods for heat dissipation are classified into the following two kinds: one is to set a coolant pipe into the rotor, and the other is to use compressed air to carry heat away from the rotor surface (as disclosed in U.S. Pat. No. 5,703,418). Both methods described above have obvious disadvantages: the former requires a coolant pipe to be set into the limited space provided by the rotor, so that the mechanism is more complicated, the manufacturing cost is higher, the volume and weight of the rotor are increased, and an extra mechanism is required to guide the flow of liquid for heat dissipation, which is not economical. The second method, which is to use compressed air to cool the surface of the rotor, is simpler than the first method, but does not dissipate heat as effectively because the heat conductivity of the closed structure used for wrapping the coils is poor, resulting in a large temperature difference between the surface of the rotor and the nearby area of the coils.
Therefore, methods for heat dissipation present a big problem in designing a linear motor.
The purpose of the present invention is to solve the disadvantages, such as poor heat dissipation ability, complicated heat dissipation mechanism, and high manufacturing cost, of the conventional coreless type linear motor. In addition, the present invention also avoids the conditions that the assembly of parts is too tight or too loose, and that the efficiency of the motor lowers due to rise in temperature after the linear motor is used for a period of time.
The method of heat dissipation in the present invention first seeks to avoid using a coolant pipe, in order to avoid the need for pipes in the rotor of the linear motor and other complicated mechanisms to make the coolant flow. Instead, for enhancing the effect of heat dissipation, the heat resistance of the heat source and surrounding is lowered. In order to achieve the reduction in heat resistance, the coils of the rotor are not designed as winding type coils but rather have openings in the centers of the coils. Although this may increase the volume slightly, heat generation is more centered such that it is easy and convenient to make the heat dissipate to the air by forming holes at the center of the coils, or in the area around the coils, and to make the holes interlink to external air. This method not only increases the contact area between the coils of the rotor and air, but also adds to the effect of heat dissipation of coils by eliminating the insulating substance that isolates the coils and prevents thermal conduction. In addition, the method reduces the weight of the rotor and increases the effective thrust of the linear motor due to the reduced mass.
Because the coils of the rotor provide the motive force of the linear motor and also suffer from counterforce, a heat sink compound with good thermal conductivity is smeared around the coils for the sake of protecting the coils. The heat sink compound can improve the thermal conductivity between the coils and the material around the coils. For the sake of further promoting the heat dissipation effect of the rotor, the heat sink compound is smeared around the heat dissipation holes to enlarge the heat dissipation area. In this way, when the rotor of the motor moves, flowing air around the rotor can efficiently carry heat away from the surface of the heat sink compound.
Some mechanisms require rotors having a structure with higher strength, in which case the heat sink compound can fill up the heat holes. Consequently, the rotor can provide a better heat dissipation effect, and have better structural strength. In order to promote a heat dissipation effect between the heat sink compound and air, ragged strips are set at the contacting surface between the heat sink compound and air to increase the heat dissipation effect.
On the other hand, a heat pipe may be fastened by the heat sink compound and buried in the heat hole. One end of the heat pipe is buried near a coil while the other end is extended to the outside of the closed structure of the coils, so that heat from the coils can be conducted easily to the outside via the heat pipes. The heat pipe is preferably made of metal having good thermal conductivity so that heat can be conducted along the heat pipe. For some airtight hollow heat pipes, the interior is designed to be almost a vacuum, and to have very good thermal conductivity. In order to make the thermal conduction effect even better, the end of the heat pipe, which is at the exterior of the closed structure of the coils can be connected with a heat sink, which is usually made of metal, and can help to transfer heat to air.